We examined the association of changes in physical activity and diet with obesity development and changes in body fat percentage, body mass index, and waist circumference. 31,344 adults without obesity at baseline (age = 56.0 ± 7.5 years; female = 49.1%) from the UK Biobank were included. Physical activity was categorised based on public health guidelines as: inactive; insufficient; and sufficient. Diet category was assigned based on an established composited score that included consumption of fruits, vegetables, fish, red meat (unprocessed), and processed meat. Diet was categorised as: poor; reasonable; and good. Physical activity and diet changes were categorised based on changes in category: worsened; stable; increased (physical activity)/improved (diet). During a mean follow up of 6.8 (SD = ±2.3) years, 1354 (4.3%) participants developed obesity. Compared to stable physical activity-diet, increasing physical activity was associated with the lowest obesity odds, across diet changes (e.g., OR [95%CI]: diet worsened (0.89 [0.69, 1.15]); diet improved (0.65 [0.48, 0.89])). Increasing physical activity with improved diet was associated with the largest difference in body fat percentage (β:-0.62 [-0.82, -0.41]), body mass index (-0.37 [-0.47, -0.28]), and waist circumference (-1.21 [-1.63, -0.79]). Excluding adults with a history of smoking, or major illness, lowered obesity odds among participants with increased physical activity by an additional 11%-21%. In those who decreased physical activity obesity was attenuated when combined with diet improvement. Improvements in physical activity or diet mutually attenuated the deleterious associations of the other behaviour's deterioration. In most analyses, increases in physical activity conferred consistent positive associations against the development of obesity, across dietary change groups.
Keywords: Adiposity; Diet; Nutrition; Obesity; Physical activity.
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